1. Field of the Invention
This invention relates to a method for releasing a molded synthetic resin product from a mold. This invention particularly relates to a method for releasing a molded synthetic resin product from a mold wherein a molded synthetic resin product, such as an optical disk sheet, which is required to exhibit a high accuracy in its flatness, is released from a mold without being deformed or damaged.
2. Description of the Prior Art
In general, when molded synthetic resin products are released from molds after being molded in the molds with injection molding processes, the molded synthetic resin products are knocked out of the molds with mechanical means such as ejector pins and ejector sleeves. However, when thin sheet-like molded products, such as optical disk sheets, are released from molds with such methods, the molded products easily become deformed. Accordingly, air pressure has heretofore been used to release the thin sheet-like molded products from the molds.
For example, in Japanese Unexamined Patent Publication No. 59(1984)-45110, a method is disclosed wherein, in the course of opening the mold, compressed air is jetted to the bottom surface of a female mold half, an edge of a male mold half, and a peripheral surface of the female mold half, in order to release a molded product from the mold with the pressure of the compressed air. Also, in Japanese Unexamined Patent Publication No. 59(1984)-176029, a method is disclosed wherein the air is jetted to an outer circumferential edge of a molded synthetic resin product on a mold until the outer circumferential part of the molded synthetic resin product floats away from the mold, and thereafter the center part of the molded synthetic resin product is released from the mold.
A product which has been molded with an injection molding process must be released from both a fixed mold half and a movable mold half, which together constitute the mold. In cases where air pressure is used to release the molded product from the mold, in order to release the molded product from the fixed mold half, air is introduced from the side of the fixed mold half to a position between a molding surface of the fixed mold half and the molded product. In order to release the molded product from the movable mold half, air is introduced from the side of the movable mold half to a position between a molding surface of the movable mold half and the molded product.
At the time the molded product is released from the mold, the temperature of the molded product is considerably high. Therefore, in cases where the molded product is a thin sheet-like product such as an optical disk sheet, the molded product, after it has been released from the mold, easily becomes deformed due to factors such as the timing with which the air is jetted to positions between the molding surfaces of the mold and the molded product, the pressure of the air, and the time during which the air is jetted. In order to prevent the molded product from being deformed, various attempts have heretofore been made to improve the accuracy of the air pressure, the accuracy of the timing with which the jetting of the air starts, the accuracy of the timing with which the jetting of the air stops, or the like. By way of example, a method has heretofore been employed wherein the molding machine is provided with timers, the jetting of the air is started and stopped with the timers, and the start and stop times are set with a molding program.
However, even when the timing with which the jetting of the air starts and the timing with which the jetting of the air stops are controlled with timers, the surface accuracy of the molded products varies among those molded with different molding shots.